This invention relates to a fluid control device, and particularly to such a device adapted for controlling operation of a motor vehicle automatic transmission.
In the past, automatic transmissions used in motor vehicles were typically controlled through fluidic control systems incorporating numerous piston and cylinder assemblies. Although such devices operate satisfactorily, they have several drawbacks including high cost attributable to the high precision necessary in machining the components and the necessity of providing and assembling numerous components. Further, such systems are restricted in their operational capabilities. Modern motor vehicles are incorporating increasing numbers of electronically controlled subsystems and particular attention is presently being directed toward designing electronically controlled automatic transmission controllers. This invention relates specifically to such a control device.
A number of significant design challenges are presented in designing an electronically operated transmission controller. Due to the fact that such controllers would typically be located within the oil sump region of the automatic transmission, the overall height of the assembly must be limited in order to provide acceptable vehicle ground clearance and to otherwise facilitate packaging of the various transmission components. It is further desirable to provide such a device which is resistant to tampering to prevent unqualified individuals from undertaking servicing operations. As with any device intended for mass production, manufacturing cost is of extreme importance. Cost advantages can be obtained through devices which are capable of being assembled using automatic machinery. Furthermore, cost savings are realized when the components of the system are not required to be manufactured with high dimensional precision. Accordingly, it is desirable to provide a transmission controller capable of being assembled automatically and which is made from components having minimal tolerance requirements.